LightningLeaders Converge in Alabama

Lightning leaders to converge on Alabama

International conference set for
June

May 24, 1999:
By the time you finish reading this sentence, lightning will
have struck more than 100 times across the Earth. Each delivers
about 1 trillion watts of electricity in manner of microseconds.
The highly conductive lightning channel heats the air to over
15,000 deg. C (27,000 deg. F), which is almost three times the
surface temperature of the sun.

Lightning also is one of the most beautiful and mysterious
events in nature, something to admire, from a safe distance -
and to study in detail.

Right: Look but don't touch (meaning
stay inside; don't stand in the open or near trees or power lines).
Lightning is as deadly as it is beautiful. Credit: Chuck Clark,
NOAA.

The Global Hydrology and Climate
Center (GHCC) will host the 11th quadrennial International Conference
on Atmospheric Electricity, June 7-11 at Guntersville State Park
in north Alabama. Scientists attending this conference study
thunderstorms, lightning and other electrical properties of the
atmosphere. This will be the first time that the conference has
been held in the Southeast.

"Traditionally, this conference has been
hosted by a group that is active in the field of atmospheric
electricity or lightning research," said Dr. Hugh Christian,
one of the lead lightning scientists at the GHCC. The GHCC fits
that criterion since its scientists are among the world leaders
in the field of atmospheric electricity and revolutionized the
field of spaced-based lightning observations from well before
the GHCC was founded in 1994.

Left:
A frame from TV images taken aboard the Space Shuttle (STS-35;
April 28, 1990) shows lightning outshining city lights - and
a sprite reaching for the top of the atmosphere. (NASA)

Beginning in 1980, scientists from this group have studied
lightning and thunderstorm from NASA's ER-2 high altitude aircraft
and later from the Space Shuttle. In the Mesoscale Lightning
Experiment, the Shuttle 's payload bay cameras observed lightning
on the nightside of the Earth during crew sleep periods.

More recent observations have been made using the Marshall-developed
Optical Transient Detector (OTD) on MicroLab 1 (launched April
3, 1995) and the Lightning Imaging Sensor (LIS) on the Tropical
Rainfall Measuring Mission (TRMM; launched Nov. 28, 1997). Christian
is the principal investigator for both instruments.

NASA and the Air Force continue
to have a deep interest because of the potential for lightning
to destroy rockets: their metal bodies and long conducting trail
of hot gas can readily trigger lightning flashes.

Despite
its fascinating nature and the damage and death it causes, only
a relatively small number of groups around the world study lightning.

Lightning distribution as seen
by the Optical Transient Detector aboard MicroLab 1 during September
1995-August 1997. (NASA/GHCC)

"The U.S. is one of the most active countries in the
field of Atmospheric Electricity," Christian said. "Japanese
scientists also are active. However, it tends to concentrate
on the physics of the lightning event, perhaps because its power
industry plays such an active role. In the United States, there
is also much interest in the meteorological aspects of the science."

In addition, groups from around the world including scientists
from Japan, Russia, Germany, France, Sweden, China and India
are actively involved in the field. The conference will be large,
with scientists from 28 countries in attendance. Christian expects
more than 200 scientists will turn out to present papers.

One of the topics they will hear is research indicating
that lightning has the potential for providing excellent real-time
information about the energy inside the storms. The classic anvil
and the "overshooting turret" cloud formations are
good indicators of convection. However, these cloud formations
provide little insight into what is happening deep in the heart
of the cloud and the anvils survive well after the convective
activity has ended.

"We think that lightning responds very rapidly to what
is happening in the center of clouds with electrical energy being
generated within minutes of changes in convective intensity,"
Christian said. The ability to monitor closely what is happening
inside the clouds could be a valuable tool for predicting what
might happen next - including the potential for a tornado.

Recent advances in radar, including
NEXRAD, have improved the weather forecaster's ability to tell
if a tornado is spinning out of a storm cell, but they still
lag in their ability to measure the vertical velocity of these
storms, which are important clues to the overall puzzle. Establishing
multiple operational Doppler radar networks around the nation
or placing fleets of weather radars in orbit is impractical.

Right: Many scientists view lightning as the most
visible (and dangerous) part of a much larger global electrical
circuit in which the ground itself is, well, the ground plane.
(NASA)

But watching for lightning from space might be a viable alternative,
Christian said. His team has been studying designs for a lightning
mapping sensor that would be added to weather satellites in geostationary
orbit. The sensor would watch the entire continent and focus
in on areas where lightning activity seems to be sharply increasing
and decreasing.

A sudden jump in activity may be the clue that scientists
have been seeking for detecting an intensifying storm that might
be a precursor to tornadoes. This dramatic increase in lightning,
signifying intensification of the storm's vertical motion is
generally followed by a sharp decrease, suggesting collapse.

On April 17, 1995,
the OTD observed a steady rise in lighting activity in a supercell
storm over Oklahoma. Just before the spacecraft passed out of
view of the storm, the lightning rates dropped sharply. A few
minutes later, a tornado was observed descending out of the storm.

Left: A tornado aims for Dimmet,
Texas. (NOAA)

The linkage is that strong upward convection leads to high
lightning rates and increased vorticity. Then the convection
collapses and generates downdrafts, leading to a sharp decrease
in the lightning and setting the conditions for the onset of
a tornado.

Validation of this effect could
enhance warning capabilities with space-based lightning sensors
providing up to 10 extra minutes more warning time for severe
weather intensification and tornadoes.

In addition to this tantalizing discovery, the GHCC's lightning
team has found that lightning loves land. Maps of global lightning
frequency shows that lightning occurs most often in storms over
land. Further, they have hypothesized that lightning loves land
because the heating of the continents creates stronger convection.

Â

Lightning likes land: Data from the Lightning Imaging Sensor
shows that most lightning strikes occur over land where the ground
can warm the air more effectively. This map is covers to the
latitudes (35 deg. N to 35 deg S) overflown by the Tropical Rainfall
Measuring Mission carrying the LIS. Links to 937x224-pixel,
37K GIF. (NASA/GHCC)

Space-based observations of lightning will be only one of
dozens of topics covered at at the Atmospheric Electricity Conference.

Several papers will be presented
on sprites, the tantalizing flashes of light that dance high
over the tops of storm, seemingly into space. While the physics
of this phenomenon is not understood, it is possible that sprites
play important roles in the global electrical circuit and upper
atmospheric chemistry. Other papers will cover the 3-dimensional
structure of lightning, the physics of charge generation and
lightning initiation, and studies of lightning variations with
weather phenomena such as El Nino. Sessions will be dedicated
to lightning characteristics, lightning detection and protection,
thunderstorm characteristics, fair weather electricity, global
lightning and lightning chemistry.